Multi-step and asymmetrically shaped laser beam scribing

ABSTRACT

Methods of dicing substrates by both laser scribing and plasma etching. A method includes laser ablating material layers, the ablating leading with a first irradiance and following with a second irradiance, lower than the first. Multiple passes of a beam adjusted to have different fluence level or multiple laser beams having various fluence levels may be utilized to ablate mask and IC layers to expose a substrate with the first fluence level and then clean off redeposited materials from the trench bottom with the second fluence level. A laser scribe apparatus employing a beam splitter may provide first and second beams of different fluence from a single laser.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 13/160,822, entitled “Multi-step and AsymmetricallyShaped Laser Beam Scribing,” and filed on Jun. 15, 2011, the entirecontents of which are hereby incorporated by reference in its entiretyfor all purposes.

TECHNICAL FIELD

Embodiments of the present invention pertain to the field ofsemiconductor processing and, in particular, to methods for dicingsubstrates, each substrate having an integrated circuit (IC) thereon.

BACKGROUND DESCRIPTION OF RELATED ART

In semiconductor substrate processing, ICs are formed on a substrate(also referred to as a wafer), typically composed of silicon or othersemiconductor material. In general, thin film layers of variousmaterials which are either semiconducting, conducting or insulating areutilized to form the ICs. These materials are doped, deposited andetched using various well-known processes to simultaneously form aplurality of ICs, such as memory devices, logic devices, photovoltaicdevices, etc, in parallel on a same substrate.

Following device formation, the substrate is mounted on a supportingmember such as an adhesive film stretched across a film frame and thesubstrate is “diced” to separate each individual device or “die” fromone another for packaging, etc. Currently, the two most popular dicingtechniques are scribing and sawing. For scribing, a diamond tippedscribe is moved across a substrate surface along pre-formed scribelines. Upon the application of pressure, such as with a roller, thesubstrate separates along the scribe lines. For sawing, a diamond tippedsaw cuts the substrate along the streets. For thin substratesingulation, such as <150 μms (μm) thick bulk silicon singulation, theconventional approaches have yielded only poor process quality. Some ofthe challenges that may be faced when singulating die from thinsubstrates may include microcrack formation or delamination betweendifferent layers, chipping of inorganic dielectric layers, retention ofstrict kerf width control, or precise ablation depth control.

While plasma dicing has also been contemplated, a standard lithographyoperation for patterning resist may render implementation costprohibitive. Another limitation possibly hampering implementation ofplasma dicing is that plasma processing of commonly encounteredinterconnect metals (e.g., copper) in dicing along streets can createproduction issues or throughput limits. Finally, masking of the plasmadicing process may be problematic, depending on, inter alia, thethickness and top surface topography of the substrate, the selectivityof the plasma etch, and the materials present on the top surface of thesubstrate.

SUMMARY

Embodiments of the present invention include methods of laser scribingsubstrates. In the exemplary embodiment, the laser scribing isimplemented as a first operation in a hybrid dicing process includingboth laser scribing and plasma etching.

In an embodiment, a method of dicing a semiconductor substrate having aplurality of ICs includes receiving a masked semiconductor substrate,the mask covering and protecting ICs on the substrate. The maskedsubstrate is ablated along streets between the ICs with a point on thesubstrate exposed to increasing irradiance. In one embodiment, at leasta portion of the mask thickness in the street is ablated throughexposure to electromagnetic radiation of first irradiance (opticalintensity) to provide a patterned mask with gaps or trenches. At least aportion of a thin film device layer stack disposed below the mask isthen ablated through exposure to electromagnetic radiation having secondirradiance to expose regions of the substrate between the ICs. The ICsare then singulated into chips, for example by plasma etching throughthe exposed substrate following the trenches in the patterned mask.

In another embodiment, a system for dicing a semiconductor substrateincludes a laser scribe module and a plasma etch chamber, integratedonto a same platform. The laser scribe module is to iteratively scribethe substrate and the plasma chamber is to etch through the substrateand singulate the IC chips. The laser scribe module may include one ormore of a multiple lasers, a multi-pass controller, or a beam shaper toscribe the substrate via exposure to a plurality of optical intensities.

In another embodiment, a method of dicing a substrate having a pluralityof ICs includes receiving a masked silicon substrate. The ICs include acopper bumped top surface having bumps surrounded by a passivationlayer, such as polyimide (PI). Subsurface thin films below the bumps andpassivation include a low-K interlayer dielectric (ILD) layer and alayer of copper interconnect, the entire set of layers comprising adevice film layer stack. A femtosecond laser ablates, throughirradiation, a predetermined pattern of trenches into the film layerstack by one or more sequential laser irradiation steps and into a thinfilm IC stack disposed below the mask with a second irradiance to exposea portion of a substrate and may further ablate into the same substratesuch that there is sufficiently small amounts of residual film layerstack remaining on the substrate at the trench bottoms. The ablationleads with a first irradiance and follows with a second irradiancegreater than, less than, or essentially equal to the first irradiance.The kerf width may additionally be reduced or increased with changingirradiance. A plasma etch is performed in a plasma etch chamber toadditionally remove substrate material below the removed film layerstack to singulate individual ICs out of the single substrate. Anyremaining mask material is then removed by a suitable method such aswashing by solvent or dry plasma cleaning.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not limitation, in the figures of the accompanying drawings inwhich:

FIG. 1 is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation method with a laser scribing process leading with afirst irradiance and following with a second irradiance, in accordancewith an embodiment of the present invention;

FIG. 2A is a flow diagram illustrating a laser scribing process whichmay be utilized in FIG. 1, in accordance with an embodiment of thepresent invention;

FIG. 2B is a flow diagram illustrating a laser scribing process whichmay be utilized in FIG. 1, in accordance with an embodiment of thepresent invention;

FIG. 2C is a flow diagram illustrating a laser scribing process whichmay be utilized in FIG. 1, in accordance with an embodiment of thepresent invention;

FIG. 3A is a graph of irradiance over time for a laser scribing process,in accordance with an embodiment of the present invention;

FIG. 3B is a graph of a spatial profile of an asymmetric laser beam fora single-pass laser scribing process, in accordance with an embodimentof the present invention;

FIG. 3C is a graph of a spatial profiles of laser beams for a multi-passlaser scribing process, in accordance with an embodiment of the presentinvention;

FIG. 4A illustrates a cross-sectional view of a substrate including aplurality of ICs corresponding to operation 101 of the dicing methodillustrated in FIG. 1, in accordance with an embodiment of the presentinvention;

FIG. 4B illustrates a cross-sectional view of a substrate including aplurality of ICs corresponding to operation 103 of the dicing methodillustrated in FIG. 1, in accordance with an embodiment of the presentinvention;

FIG. 4C illustrates a cross-sectional view of a substrate including aplurality of ICs corresponding to operation 104 of the dicing methodillustrated in FIG. 1, in accordance with an embodiment of the presentinvention;

FIG. 4D illustrates a cross-sectional view of a semiconductor substrateincluding a plurality of ICs corresponding to operation 105 of thedicing method illustrated in FIG. 1, in accordance with an embodiment ofthe present invention;

FIG. 5 illustrates an expanded cross-sectional view of an mask and thinfilm device layer stack ablated by a laser and plasma etched, inaccordance with embodiments of the present invention;

FIG. 6A illustrates a block diagram of an integrated platform layout forlaser and plasma dicing of substrates, in accordance with an embodimentof the present invention; and

FIG. 6B illustrates a block diagram of a laser scribing module for laserscribing, in accordance with an embodiment of the present invention;

FIG. 7 illustrates a block diagram of an exemplary computer system whichcontrols automated performance of one or more operation in the laserscribing methods described herein, in accordance with an embodiment ofthe present invention;

FIG. 8A is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation method with a laser scribing process leading with afirst irradiance and following with a second irradiance lower than thefirst irradiance, in accordance with an embodiment of the presentinvention;

FIGS. 8B, 8C, and 8D illustrate cross-sectional views of a substratecorresponding to operations of the dicing method illustrated in FIG. 8A,in accordance with an embodiment of the present invention

FIG. 9A is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation method with a split beam laser scribing process leadingwith a first irradiance and following with a second irradiance, inaccordance with an embodiment of the present invention;

FIG. 9B illustrates a schematic diagram of a laser scribing module forsplit beam laser scribing, in accordance with an embodiment of thepresent invention; and

FIG. 10 illustrates a schematic of a beam-splitter, in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION

Methods of dicing substrates, each substrate having a plurality of ICsthereon, are described. In the following description, numerous specificdetails are set forth, such as femtosecond laser scribing and deepsilicon plasma etching conditions in order to describe exemplaryembodiments of the present invention. However, it will be apparent toone skilled in the art that embodiments of the present invention may bepracticed without these specific details. In other instances, well-knownaspects, such as IC fabrication, substrate thinning, taping, etc., arenot described in detail to avoid unnecessarily obscuring embodiments ofthe present invention. Reference throughout this specification to “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” in various places throughout thisspecification are not necessarily referring to the same embodiment ofthe invention. Furthermore, the particular features, structures,materials, or characteristics may be combined in any suitable manner inone or more embodiments. Also, it is to be understood that the variousexemplary embodiments shown in the Figures are merely illustrativerepresentations and are not necessarily drawn to scale.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe structural relationships between components.It should be understood that these terms are not intended as synonymsfor each other. Rather, in particular embodiments, “connected” may beused to indicate that two or more elements are in direct physical orelectrical contact with each other. “Coupled” my be used to indicatethat two or more elements are in either direct or indirect (with otherintervening elements between them) physical or electrical contact witheach other, and/or that the two or more elements co-operate or interactwith each other (e.g., as in a cause an effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one material layer with respect to other materiallayers. As such, for example, one layer disposed over or under anotherlayer may be directly in contact with the other layer or may have one ormore intervening layers. Moreover, one layer disposed between two layersmay be directly in contact with the two layers or may have one or moreintervening layers. In contrast, a first layer “on” a second layer is incontact with that second layer. Additionally, the relative position ofone layer with respect to other layers is provided assuming operationsare performed relative to a substrate without consideration of theabsolute orientation of the substrate.

Generally, described herein is a laser scribe process employing aplurality of optical intensities to cleanly ablate a predetermined paththrough an unpatterned (i.e., blanket) mask layer, a passivation layer,and subsurface thin film device layers. The laser scribe process maythen be terminated upon exposure of, or partial ablation of, thesubstrate. The ablation processing employs first of a plurality ofoptical intensities to remove upper layers (e.g., mask and thin filmdevice layers) which are more easily damaged relative to the substrateand/or other thin film device layers. Subsequent ablation down to andincluding a portion of the substrate may then proceed without exposingthe easily damaged layers to the higher intensity radiation employed. Asemployed herein the term “iterative ablation” refers to an ablationprocess which exposes a point on a substrate to laser radiation having aplurality of optical intensities.

In accordance with an embodiment of the present invention, at least aportion of the iterative laser scribing process employs a femtosecondlaser. Femtosecond laser scribing is an essentially, if not completely,non-equilibrium process. For example, the femtosecond-based laserscribing may be localized with a negligible thermal damage zone. In anembodiment, femtosecond laser scribing is used to singulate ICs havingultra-low κ films (i.e., with a dielectric constant below 3.0). In oneembodiment, direct writing with a laser eliminates a lithographypatterning operation, allowing the masking material to be somethingother than a photo resist as is used in photolithography. In theexemplary hybrid dicing embodiment, an iterative laser scribing processis followed by a plasma etch through the bulk of the substrate. In onesuch embodiment, a substantially anisotropic etching is used to completethe dicing process in a plasma etch chamber; the anisotropic etchachieving a high directionality into the substrate by depositing onsidewalls of the etched trench an etch polymer.

FIG. 1 is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation method 100 employing iterative laser scribing, inaccordance with an embodiment of the present invention. FIGS. 4A-4Dillustrate cross-sectional views of a substrate 406 including first andsecond ICs 425, 426 corresponding to the operations in method 100, inaccordance with an embodiment of the present invention.

Referring to operation 101 of FIG. 1, and corresponding FIG. 4A, asubstrate 406 is received. The substrate 406 includes a mask 402covering a thin film device layer stack 401 comprising a plurality ofdistinct materials found both in the ICs 425, 426 and intervening street427 between the ICs 425, 426. Generally, the substrate 406 is composedof a material suitable to withstand a fabrication process of the thinfilm device layers formed thereon and may also have other propertyrequirements, for example, in silicon-based transistor ICs, where thesubstrate forms a part of active devices. For example, in oneembodiment, substrate 406 is a group IV-based material such as, but notlimited to, monocrystalline silicon, germanium or silicon/germanium. Inanother embodiment, substrate 406 is a III-V material such as, e.g., aIII-V material substrate used in the fabrication of light emittingdiodes (LEDs). During device fabrication, the substrate 406 is typically600 μm-800 μm thick, but as illustrated in FIG. 4A may have been thinnedto less than 400 μm and sometimes thinner than 150 um with the thinnedsubstrate now supported by a carrier 411, such as a backing tape 410stretched across a support structure of a dicing frame (not illustrated)and adhered to a backside of the substrate with a die attach film (DAF)408.

In embodiments, first and second ICs 425, 426 include memory devices orcomplimentary metal-oxide-semiconductor (CMOS) transistors fabricated ina silicon substrate 406 and encased in a dielectric stack. A pluralityof metal interconnects may be formed above the devices or transistors,and in surrounding dielectric layers, and may be used to electricallycouple the devices or transistors to form the ICs 425, 426. Materialsmaking up the street 427 may be similar to or the same as thosematerials used to form the ICs 425, 426. For example, street 427 mayinclude thin film layers of dielectric materials, semiconductormaterials, and metallization. In one embodiment, the street 427 includesa test device similar to the ICs 425, 426. The width of the street 427may be anywhere between 10 μm and 200 μm, measured at the thin filmdevice layer stack/substrate interface.

In embodiments, the mask 402 may be one or more material layersincluding any of a plasma deposited polymer (e.g., C_(x)F_(y)), a watersoluble material (e.g., poly(vinyl alcohol)), a photoresist, or similarpolymeric material which may be removed without damage to an underlyingpassivation layer, which is often polyimide (PI) and/or bumps, which areoften copper. The mask 402 is to be of sufficient thickness to survive aplasma etch process (though it may be very nearly consumed) and therebyprotect the copper bumps which may be damaged, oxidized, or otherwisecontaminated if exposed to the substrate etching plasma.

FIG. 5 illustrates an expanded cross-sectional view 500 of a bi-layermask including a mask layer 402B (e.g., C_(x)F_(y) polymer) applied overa mask layer 402A (e.g., a water soluble material) in contact with a topsurface of the IC 426 and the street 427, in accordance with embodimentsof the present invention. As shown in FIG. 5, the substrate 406 has atop surface 503 upon which thin film device layers are disposed which isopposite a bottom surface 502 which interfaces with the DAF 408 (FIG.4A). Generally, the thin film device layer materials may include, butare not limited to, organic materials (e.g., polymers), metals, orinorganic dielectrics such as silicon dioxide and silicon nitride. Theexemplary thin film device layers illustrated in FIG. 5 include asilicon dioxide layer 504, a silicon nitride layer 505, copperinterconnect layers 508 with low-κ (e.g., less than 3.5) or ultra low-κ(e.g., less than 3.0) interlayer dielectric layers 507 (ILD) such ascarbon doped oxide (CDO) disposed there between. A top surface of the IC426 includes a bump 512, typically copper, surrounded by a passivationlayer 511, typically a polyimide (PI) or similar polymer. The bump 512and passivation layer 511 therefore make up a top surface of the IC withthe thin film device layers forming subsurface IC layers. The bump 512extends from a top surface of the passivation layer 511 by a bump heightH_(B) which in the exemplary embodiments ranges between 10 μm and 50 μm.One or more layers of the mask may not completely cover a top surface ofthe bump 512.

Referring back to FIG. 1, at operation 103 a predetermined pattern isdirectly written into the mask 402 with a first ablation along acontrolled path relative to the substrate 406. As illustrated incorresponding FIG. 4B, the mask 402 is patterned in the first ablationby laser radiation 411 to form trench 414A extending through at least aportion of the mask thickness. In the exemplary embodiment illustratedin FIG. 5, the laser scribing depth D_(L1) is approximately in the rangeof 5 μm to 30 μm deep, advantageously in the range of 10 μm to 20 μmdeep, depending on the thickness of the mask layers 402A and 402B. Thefirst irradiance I₁ is insufficient to ablate some layer of the thinfilm device layer stack 401 and therefore at least some portion of thethin film device layer stack 401 remains at the bottom of the trench414A following operation 103. In one such embodiment, the firstirradiance I₁ is insufficient to ablate an interconnect metal (e.g.,interconnect copper layer 508) and/or a dielectric layer (e.g., silicondioxide layer 504) of the thin film device layer stack 401.

At operation 104, the predetermined pattern is directly written with asecond ablation iteration along the controlled path relative to thesubstrate 406. Referring to the exemplary embodiment in FIG. 4C, thesubstrate 406 is exposed to the second ablation iteration by laserradiation 412 forming trench 414B extending through at least a portionof the thin film device layer stack 401. In a first embodiment, asillustrated in FIG. 5, the laser scribing depth D_(L2) is againapproximately in the range of 5 μm to 30 μm deep, advantageously in therange of 10 μm to 20 μm deep, depending on the thickness of the masklayers 402A and 402B to expose the substrate.

Depending on the embodiment the laser radiation 412 (FIG. 4C) has asecond irradiance I₂ that is either same or different than the firstirradiance I₁. In embodiments where the irradiance I₂ is the same as I₁,successive scribing allows for total energy applied to be spread overtime to reduce damage of the scribing process. For certain suchembodiments, kerf width may be different between I₁ and I₂ for furtherimprovement in cleanliness of the ablated edge. In a first embodimentwhere the irradiance I₂ is different than I₁, the irradiance I₂ isgreater than I₁, for example with the second irradiance I₂ sufficient toablate an interconnect metal and/or a dielectric layer of the thin filmdevice layer stack 401. In the exemplary embodiment, the secondirradiance I₂ is sufficient to ablate every layer of the thin filmdevice layer stack 401 and therefore operation 103 leaves the substrate406 exposed at the bottom of the trench 414B. In a further embodiment,the second irradiance is sufficient to ablate a portion of the substrate406, (e.g., single crystalline silicon) to extend the bottom of thetrench 414B below the top surface of the substrate 406.

As further illustrated in FIGS. 4B 4C, the trench 414A has a first kerfwidth (KW₁) which is a function of a beam width possessing an energygreater than a threshold associated for the particular material of themask 402 and the trench 414B has a second kerf width KW₂ as function ofa beam width possessing an energy greater than a greatest thresholdassociated for the materials in the thin film device layer stack 401. Ina first embodiment, the first kerf width KW₁ is larger than the secondkerf width KW₂ so the mask 402 and upper layers of the thin film devicestack 401 ablated at the first irradiance I₁ are not further disturbedby ablation of the underlying material layers ablated at the higherirradiance I₂. Notably in the exemplary embodiment, the entire firstkerf width KW₁ is ablated to substantially the same depth as no pointwithin the beam profile defining the kerf width KW₁ (perpendicular todirection of travel) has sufficient irradiance to ablate the entirethickness of the device stack. This is in contrast to a beam having aGaussian spatial profile having a first irradiance at an outer perimeterof the beam diameter and a second irradiance within an inner diameter ofthe beam so that as the beam travels the leading edge of the beam makesa first kerf width KW₁ smaller than that of the inner beam diameter. Incertain such embodiments, the second width KW₂ is between 10% and 50%smaller than the second kerf width KW₂. As one exemplary embodiment, thefirst kerf width KW₁ is less than 15 μm while the second kerf width KW₂is 6 μm to 10 μm.

FIG. 3A is a graph of irradiance over time for an iterative laserscribing process, in accordance with an embodiment of the presentinvention. As shown, irradiance (W/cm²) curve 305 is plotted for aparticular point on the substrate along the ablation path. Beginning attime t₀, the point is exposed to radiation having a first irradiance I₁for the duration of a leading portion 315. At time t₁, irradiation ofthe radiation increases above a threshold T, for example the thresholdenergy of a single crystalline substrate material, T_(Si), where theablation rate begins to increase substantially, which might generally bein the range of 0.01 GW/cm² and 1 GW/cm². Beginning at time t₁, thepoint is exposed to radiation having a second irradiance I₂ for theduration of a trailing portion 310, ending at time t₂. For the exemplaryembodiment, the second irradiance I₂ is above the threshold energy of asingle crystalline substrate material, T_(Si). In alternate embodiments,the threshold between I₁ and I₂ is demarked by a threshold associatedfor any of the mask material (generally in the range of 0.0001 GW/cm²and 0.001 GW/cm²), dielectric layer of the thin film device layer stack401 (generally in the range of 0.1 GW/cm² and 10 GW/cm²), or aninterconnect layer of the thin film device layer stack 401 (generally bein the range of 0.01 G W/cm² and 0.1 GW/cm²).

Iterative ablation (e.g., operations 103 and 104) may be implemented ina number of manners to achieve the change in irradiance illustrated inFIG. 3A. In one embodiment, a laser beam is shaped to have a spatiallyvarying irradiance profile along a direction of travel with the firstportion providing the first ablation iteration and second portionproviding the second ablation iteration. FIG. 3B is a graph of a spatialprofile 320 of an asymmetrically shaped laser beam for a single-passiterative laser scribing process, in accordance with an embodiment ofthe present invention. With power (P) plotted along the dimension x,with x increasing along a direction of travel, the spatial profile 320includes a leading edge portion 315 and a trailing edge portion 310. Theleading portion 315 has a lower power (P) than the trailing portion 310to provide a first irradiance I₁ spanning the distance x₁ to x₂ while asecond irradiance I₂ spans the distance x₀ to x₁. With x₀ to x₂representing the beam width along the direction of travel (whethermeasured by D4σ, 10/90 knife-edge, 1/e2, FWHM, etc.) for a given widthperpendicular to the direction of travel (i.e., y), in the exemplaryembodiment illustrated, the trailing edge portion 310 is off-centerwithin the beam width along the direction of travel (i.e.,asymmetrical). As further shown in FIG. 3B, at x₁, power exceeds thethreshold energy associated with a silicon substrate T_(Si) such thatthe leading portion 315 does not have sufficient energy to ablate theentire thin film device layer stack 401 while the trailing portion 310does have sufficient energy to ablate the entire thin film device layerstack 401 as well as a portion of a silicon substrate.

FIG. 2A is a flow diagram illustrating an iterative laser scribingprocess 200 using a beam with a profile shaped as shown in FIG. 3B toimplement the first iteration (operation 103) and second iteration(operation 104) in the method 100 (FIG. 1) with a single beam and asingle pass. Referring to FIG. 2A, a single beam is generated atoperation 201. In an embodiment, the beam has a pulse width (duration)in the femtosecond range (i.e., 10⁻¹⁵ seconds), referred to herein as afemtosecond laser. Laser parameters selection, such as pulse width, maybe critical to developing a successful laser scribing and dicing processthat minimizes chipping, microcracks and delamination in order toachieve clean laser scribe cuts. A laser pulse width in the femtosecondrange advantageously mitigates heat damage issues relative to longerpulse widths (e.g., picosecond or nanosecond). Although not bound bytheory, as currently understood a femtosecond energy source avoids lowenergy recoupling mechanisms present for picosecond sources and providesfor greater thermal nonequilibrium than does a nanosecond-source. Withnanosecond or picoseconds laser sources, the various thin film devicelayer materials present in the street 427 behave quite differently interms of optical absorption and ablation mechanisms. For example,dielectrics layers such as silicon dioxide, is essentially transparentto all commercially available laser wavelengths under normal conditions.By contrast, metals, organics (e.g., low-K materials) and silicon cancouple photons very easily, particularly nanosecond-based orpicosecond-based laser irradiation. If non-optimal laser parameters areselected, in a stacked structures that involve two or more of aninorganic dielectric, an organic dielectric, a semiconductor, or ametal, laser irradiation of the street 427 may disadvantageously causedelamination. For example, a laser penetrating through high bandgapenergy dielectrics (such as silicon dioxide with an approximately of 9eV bandgap) without measurable absorption may be absorbed in anunderlying metal or silicon layer, causing significant vaporization ofthe metal or silicon layers. The vaporization may generate highpressures potentially causing severe interlayer delamination andmicrocracking. Femtosecond-based laser irradiation processes have beendemonstrated to avoid or mitigate such microcracking or delamination ofsuch material stacks.

In an embodiment, the laser source for operation 201 has a pulserepetition rate approximately in the range of 200 kHz to 10 MHz,although preferably approximately in the range of 500 kHz to 5 MHz. Thelaser emission generated at operation 201 may span any combination ofthe visible spectrum, the ultra-violet (UV), and/or infra-red (IR)spectrums for a broad or narrow band optical emission spectrum. Even forfemtosecond laser ablation, certain wavelengths may provide betterperformance than others depending on the materials to be ablated. In aspecific embodiment, a femtosecond laser suitable for semiconductorsubstrate or substrate scribing is based on a laser having a wavelengthof approximately less than or equal to 1570-200 nanometers, althoughpreferably in the range of 540 nanometers to 250 nanometers. In aparticular embodiment, pulse widths are less than or equal to 400femtoseconds for a laser having a wavelength less than or equal to 540nanometers. In an alternative embodiments, dual laser wavelengths (e.g.,a combination of an IR laser and a UV laser) are used to generate thebeam at operation 201. In an embodiment, the laser source delivers pulseenergy at the work surface approximately in the range of 0.5 μJ to 100μJ, although preferably approximately in the range of 1 μJ to 5 μJ.

At operation 205, the generated beam is shaped to vary an opticalintensity (irradiance) spatial profile as exemplified by FIG. 3B. Anytechnique known in the art for providing asymmetric spatial profile maybe applied at operation 205. For example, known beam shaping optics maybe utilized to generate an elliptical beam with the major axis along thedirection of travel. In an embodiment, the elliptical beam has a majoraxis which is at least 1.5 times longer the minor beam axis.Alternatively, coma may be purposefully introduced in order to create aspatial profile as described in FIG. 3A-3C. Additional known beamshaping techniques may be applied at operation 205 along with knowngeneration techniques at operation 201 to provide the change inintensity, or irradiance, between a leading and trailing portions of theelliptical beam's major axis to provide the asymmetrical profileillustrated in FIG. 3B.

At operations 210 and 215, the spatially shaped beam is controlled totravel a predetermined path relative to the substrate to ablate a pointon the mask 402 first with the leading portion of the beam (e.g., asillustrated in FIG. 4B) and to subsequently ablate any underlying thinfilm device stack disposed over the substrate at that point with thetrailing portion of the beam (e.g., as illustrated in FIG. 4C). In anembodiment, the laser scribing process runs along a work piece surfacein the direction of travel at a speed approximately in the range of 200mm/sec to 5 msec, although preferably approximately in the range of 300mm/sec to 2 msec. At operation 220, method 200 returns to FIG. 1 forplasma etch of the exposed substrate.

FIG. 3C is a graph of a spatial profiles 330 and 340 to implement theoperations 103 104 in the method 100 (FIG. 1) in a multi-pass embodimentof the present invention. As shown in FIG. 3C, a plurality of beams areprovided, each with a different spatial profile. A first profile along abeam width W has a Gaussian 330 or top hat 335 shape with a maximumpower (P) below a threshold energy (e.g., T_(Si) in reference to anablation energy threshold of silicon substrate) while a second beamprofile along that same width W has a Gaussian 340 or top hat 345 shapewith a maximum power (P) above that threshold energy. As furtherillustrated in FIG. 3C, the spatial profile 340, 345 associated with thehigher irradiance has a power which exceeds the threshold energy(T_(Si)) over a width W₂ which is less than an equivalently determinedwidth W₁ for the spatial profile 330, 335 associated with the lowerirradiance.

FIG. 2B is a flow diagram illustrating a laser scribing method 250 usinga plurality of beam profiles shaped as shown in FIG. 3C to implement thefirst iteration (operation 103) and second iteration (operation 104) inthe method 100 (FIG. 1) with multiple passes of a single beam. Referringto FIG. 2B, a single beam is generated at operation 225 to have a firstirradiance. The beam generation may proceed substantially as previouslydescribed for operation 201, for example employing the same femtosecondpulse widths, wavelengths, pulse rates, etc, a beam with a firstirradiance I₁, (e.g., Gaussian 330 from FIG. 3C) is generated. Atoperation 230 the beam is moved along a predetermined path to ablatetrenches into the mask, substantially as illustrated in FIG. 4B. In anembodiment, the laser scribing operation 230 runs along a work piecesurface in the direction of travel at a speed approximately in the rangeof 500 mm/sec to 5 msec, although preferably approximately in the rangeof 600 mm/sec to 2 msec.

At operation 240, the beam is adjusted to have the second irradiance,I₂, (e.g., Gaussian 340 from FIG. 3C) is generated. The adjusted beamretraces the same predetermined path to expose the substrate atoperation 245 substantially as illustrated in FIG. 4C at substantiallythe same rate as for operation 240. At operation 249, method 250 returnsto FIG. 1 for subsequent plasma etch of the exposed substrate.

FIG. 2C is a flow diagram illustrating an iterative laser scribingprocess 290 using a plurality of beam profiles shaped as shown in FIG.3C to implement the first iteration (operation 103) and second iteration(operation 104) in the method 100 (FIG. 1) with successive passes ofbeams from a plurality of lasers. Referring to FIG. 2C, a first lasergenerates a beam with a first irradiance I₁ (e.g., Gaussian 330 fromFIG. 3B) is generated at operation 255. The beam generation may proceedsubstantially as previously described for operation 201, for exampleemploying the same femtosecond pulse widths, wavelengths, pulse rates,etc. In a preferred embodiment however, the laser utilized at operation255 has a substantially larger pulse width and may even be a continuouswave (CW) source because of the relative ease by which the trenches maybe ablated into a masking material. At operation 260, the first beam ismoved along a predetermined path to ablate trenches into the mask,substantially as illustrated in FIG. 4B.

At operation 265, a second laser generates a second beam with a secondirradiance. Generation of the second beam with the second irradiance I₂(e.g., Gaussian 335 from FIG. 3B) may proceed substantially aspreviously described for operation 201, for example employing the samefemtosecond pulse widths, wavelengths, pulse rates, etc. In a particularembodiment, where the first laser generates a first pulse train having afirst pulse width (CW) at a first wavelength, the second laser generatesa second pulse train having a second pulse width and a secondwavelength, with at least one of the second pulse width and secondwavelength being different than the first pulse width and firstwavelength. For example, in the exemplary embodiment where a CW laser isutilized at scribing operation 260, a femtosecond laser generates thesecond beam at operation 265.

At operation 270 the second laser beam is moved along the samepredetermined path to completely ablate the thin film device stack andexpose the substrate, substantially as illustrated in FIG. 4C. In anembodiment, the laser scribing operation 270 has both laser beamsrunning along the substrate simultaneously, each with speed in thedirection of travel being approximately in the range of 500 mm/sec to 5msec, although preferably approximately in the range of 600 mm/sec to 2msec. At operation 275, method 290 returns to FIG. 1 for plasma etch ofthe exposed substrate.

Returning to FIGS. 1 and 4D, the substrate 406 is exposed to a plasma416 to etch through the trenches 414 in the mask 402 to singulate theICs 426 at operation 105. In the exemplary in-situ mask depositionembodiment, the substrate is etched in the same chamber that performedthe plasma mask deposition operation 102. In accordance with anembodiment of the present invention, etching the substrate 406 atoperation 105 includes etching the trenches 414B formed with the laserscribing process to ultimately etch entirely through substrate 406, asdepicted in FIG. 4D.

In one embodiment, the etch operation 105 entails a through via etchprocess. For example, in a specific embodiment, the etch rate of thematerial of substrate 406 is greater than 25 μms per minute. Ahigh-density plasma source operating at high powers may be used for theplasma etching operation 105. Exemplary powers range between 3 kW and 6kW, or more.

In an exemplary embodiment, a deep silicon etch (i.e., such as a throughsilicon via (TSV) etch) is used to etch a single crystalline siliconsubstrate or substrate 406 at an etch rate greater than approximately40% of conventional silicon etch rates while maintaining essentiallyprecise profile control and virtually scallop-free sidewalls. Effects ofthe high power on any water soluble material layer present in the mask402 are controlled through application of cooling power via anelectrostatic chuck (ESC) chilled to −10° C. to −15° C. to maintain thewater soluble mask material layer at a temperature below 100° C. andpreferably between 70° C. and 80° C. throughout the duration of theplasma etch process. At such temperatures, water solubility isadvantageously maintained.

In a specific embodiment, the plasma etch operation 105 further entailsa plurality of protective polymer deposition cycles interleaved overtime with a plurality of etch cycles. The duty cycle may vary with theexemplary duty cycle being approximately 1:1-1:2 (etch:dep). Forexample, the etch process may have a deposition cycle with a duration of250 msec-750 msec and an etch cycle of 250 msec-750 msec. Between thedeposition and etch cycles, an etching process chemistry, employing forexample SF₆ for the exemplary silicon etch embodiment, is alternatedwith a deposition process chemistry employing a polymerizingfluorocarbon (C_(x)F_(y)) gas such as, but not limited to, C₄F₆ or C₄F₈or fluorinated hydrocarbon (CH_(x)F_(y) with x>=1), or XeF₂. Processpressures may further be alternated between etch and deposition cyclesto favor each in the particular cycle, as known in the art.

At operation 107, method 300 is completed with removal of the mask 402.In an embodiment, a water soluble mask layer is washed off with water,for example with a pressurized jet of de-ionized water or throughsubmergence in an ambient or heated water bath. In alternativeembodiments, the mask 402 may be washed off with aqueous solventsolutions known in the art to be effective for etch polymer removal.Either of the plasma singulation operation 105 or mask removal processat operation 107 may further pattern the die attach film 408, exposingthe top portion of the backing tape 410.

A single integrated process tool 600 may be configured to perform manyor all of the operations in the hybrid laser ablation-plasma etchsingulation process 100. For example, FIG. 6 illustrates a block diagramof a cluster tool 606 coupled with laser scribe apparatus 610 for laserand plasma dicing of substrates, in accordance with an embodiment of thepresent invention. Referring to FIG. 6, the cluster tool 606 is coupledto a factory interface 602 (FI) having a plurality of load locks 604.The factory interface 602 may be a suitable atmospheric port tointerface between an outside manufacturing facility with laser scribeapparatus 610 and cluster tool 606. The factory interface 602 mayinclude robots with arms or blades for transferring substrates (orcarriers thereof) from storage units (such as front opening unifiedpods) into either cluster tool 606 or laser scribe apparatus 610, orboth.

A laser scribe apparatus 610 is also coupled to the FI 602. FIG. 6Billustrates an exemplary functional block diagram of the laser scribeapparatus 610. In an embodiment illustrated in FIG. 6B, the laser scribeapparatus 610 includes a femtosecond laser 665. The femtosecond laser665 is to performing the laser ablation portion of the hybrid laser andetch singulation process 100. Relative motion between a laser beam andsubstrate to generate a scribe line can be realized either by moving thelaser beam spot, by moving the substrate, or a combination of both. Inone embodiment, a moveable stage (not depicted) for supporting thesubstrate 406 is also included in laser scribe apparatus 610, themoveable stage is configured for moving the substrate 406 (or a carrierthereof) relative to the femtosecond laser 665. As further illustrated,the laser scribe apparatus includes a scanner 670 (e.g., galvanometer)with a mirror movable to scan the laser beam in response to controlsignals from the controller 680. Between the femtosecond laser 665 andscanner 670 are beam shaping optics 660 which in one embodiment providean asymmetrically shaped beam profile substantially as shown in FIG. 3Bto perform the iterative laser scribing process 200. In furtherembodiments, the controller 680 is coupled to the femtosecond laser 665to modulate irradiance of the femtosecond laser 665 across a pluralityof non-zero irradiances over time, substantially as illustrated in FIG.3A, and/or over space substantially as illustrated in FIG. 3C to performthe scribing method 250. In another embodiment, the laser scribeapparatus 610 further includes a second laser 666 which may befemtosecond or otherwise. The second laser 666 is coupled to thecontroller 680 and each of the lasers 665 and 666 are operated throughthe scanner 670 successively in time, or simultaneously through separatescanners (i.e., scanner 670 is replicated for completely separateoptical paths between the substrate 406 and the lasers), with thecontroller 680 to direct iterative ablation over substantially the samepath to perform the scribing process 290.

Returning to FIG. 6A, the cluster tool 606 includes one or more plasmaetch chambers 608 coupled to the FI by a robotic transfer chamber 650housing a robotic arm for in-vaccuo transfer of substrates between thelaser scribe apparatus 610, plasma etch chamber 608 and/or mask module612. The plasma etch chambers 608 is suitable for at least the plasmaetch portion of the hybrid laser and etch singulation process 100 andmay further deposit a polymer mask over the substrate. In one exemplaryembodiment, the plasma etch chamber 608 is further coupled to an SF₆ gassource and at least one of a C₄F₈, C₄F₆, or CH₂F₂ source. In a specificembodiment, the one or more plasma etch chambers 608 is an AppliedCentura® Silvia™ Etch system, available from Applied Materials ofSunnyvale, Calif., USA, although other suitable etch systems are alsoavailable commercially. The Applied Centura® Silvia™ Etch systemprovides capacitive and inductive RF coupling for independent control ofthe ion density and ion energy than possible with capacitive couplingonly, even with the improvements provided by magnetic enhancement. Thisenables one to effectively decouple the ion density from ion energy, soas to achieve relatively high density plasmas without the high,potentially damaging, DC bias levels, even at very low pressures (e.g.,5-10 mTorr). This results in an exceptionally wide process window.However, any plasma etch chamber capable of etching silicon may be used.In an embodiment, more than one plasma etch chamber 608 is included inthe cluster tool 606 portion of the single integrated process tool 600to enable high manufacturing throughput of the singulation or dicingprocess.

The cluster tool 606 may include other chambers suitable for performingfunctions in the hybrid laser ablation-plasma etch singulation process100. In the exemplary embodiment illustrated in FIG. 6, a mask module612 includes any commercially available spin coating module forapplication of the water soluble mask layer described herein. The spincoating module may include a rotatable chuck adapted to clamp by vacuum,or otherwise, a thinned substrate mounted on a carrier such as backingtape mounted on a frame.

FIG. 7 illustrates a computer system 700 within which a set ofinstructions, for causing the machine to execute one or more of thescribing methods discussed herein may be executed. The exemplarycomputer system 700 includes a processor 702, a main memory 704 (e.g.,read-only memory (ROM), flash memory, dynamic random access memory(DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), astatic memory 706 (e.g., flash memory, static random access memory(SRAM), etc.), and a secondary memory 718 (e.g., a data storage device),which communicate with each other via a bus 730.

Processor 702 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processor 702 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,etc. Processor 702 may also be one or more special-purpose processingdevices such as an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. Processor 702 is configured to executethe processing logic 726 for performing the operations and stepsdiscussed herein.

The computer system 700 may further include a network interface device708. The computer system 700 also may include a video display unit 710(e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), analphanumeric input device 712 (e.g., a keyboard), a cursor controldevice 714 (e.g., a mouse), and a signal generation device 716 (e.g., aspeaker).

The secondary memory 718 may include a machine-accessible storage medium(or more specifically a computer-readable storage medium) 731 on whichis stored one or more sets of instructions (e.g., software 722)embodying any one or more of the methodologies or functions describedherein. The software 722 may also reside, completely or at leastpartially, within the main memory 704 and/or within the processor 702during execution thereof by the computer system 700, the main memory 704and the processor 702 also constituting machine-readable storage media.The software 722 may further be transmitted or received over a network720 via the network interface device 708.

The machine-accessible storage medium 731 may also be used to storepattern recognition algorithms, artifact shape data, artifact positionaldata, or particle sparkle data. While the machine-accessible storagemedium 731 is shown in an exemplary embodiment to be a single medium,the term “machine-readable storage medium” should be taken to include asingle medium or multiple media (e.g., a centralized or distributeddatabase, and/or associated caches and servers) that store the one ormore sets of instructions. The term “machine-readable storage medium”shall also be taken to include any medium that is capable of storing orencoding a set of instructions for execution by the machine and thatcause the machine to perform any one or more of the methodologies of thepresent invention. The term “machine-readable storage medium” shallaccordingly be taken to include, but not be limited to, solid-statememories, and optical and magnetic media.

It has been found that while is feasible to keep laser beam irradiance(or fluence assuming a fixed pulse width) at fixed moderate level formultiple passes to generate clean etch trenches, the range of laserpower (or pulse energy) levels associated with the optimized fluencelevel is narrow. This has the practical effect of rendering the laserscribing process window relatively small. It has also been found that afixed high fluence for multiple passes produces a relatively poor trenchtopology currently thought to be attributable to a second laser passredepositing ablated materials onto the trench formed by a first pass.

While a clean trench can be formed with a multiple pass scribing processwhere a low fluence is employed in the first pass to remove only maskand polyimide layers with limited damage/ablation of an underlying thinfilm IC layer (more particularly a dielectric layer), and the a highfluence is subsequently employed to remove the device layers to exposethe substrate (as in the method 100 illustrated in FIG. 1), delaminationmay occur. Additional high fluence passes may not always repair orremove such delamination. Though not bound by theory, it is currentlythought that in a “low-fluence first” multi-step scribing process, aportion of laser energy in the first pass transmits through thedielectric materials and causes melting/evaporation of metals in thedevice layer or substrate crystal (e.g., silicon) interfacing with thedielectric layer(s). At low fluence level, ablation of polymers reliesprimarily on linear absorption of laser energy. Because many polymermasking and passivation materials have a high light transmission ratio(a few tens percent) even for 300 nm UV wavelengths while the ablationthreshold of some metals and some substrates (e.g., silicon) is veryclose to that of many polymers, laser photons transmitted through thedielectric layer(s) of a thin film devices stack may cause delaminationat a dielectric-metal and/or dielectric-substrate interface

In certain embodiments therefore, the scribing method includes a first(second, third, etc.) pass at a high irradiance (fluence) level toablate and remove the materials in the trench to expose the substrateand then a second (third, fourth, etc.) pass at a low irradiance(fluence) level to remove debris and residues left over in the ablatedtrench without significant damage to the substrate. This type of“high-fluence-first” process may render a clean exposed substratesurface with a wider process window than either a fixed fluence multiplepass process or a low-fluence-first process. As mask or polymericpassivation layers get thicker relative to the scribe trench width(e.g., width is reduced or layer thickness is increased), ahigh-fluence-first approach becomes more advantageous.

FIG. 8A is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation method 801 in which a laser scribing process leads witha first irradiance and follows with a second irradiance that is lowerthan the first irradiance, in accordance with an embodiment of thepresent invention. Method 801 begins with a masked substrate atoperation 101, as described elsewhere herein. An exemplary substrate isillustrated by the cross-sectional view in FIG. 4A.

At operation 255, a first beam having the first irradiance is generatedat operation 255. The beam is generated in any of the manners describedelsewhere herein. In one embodiment, a laser having a predeterminedpulse width, such as the femtosecond pulse widths described elsewhereherein, is operated at a first fluence level no less than 1.0 μJ, andpreferably 1.5 μJ or higher for a 10 μm diameter spot size to achievethe first irradiance. This fluence level range is sufficient to ablatedielectric layers of the thin film IC stack (e.g., layers 504 and 507 inFIG. 5). In one femtosecond laser beam embodiment with a focused spotdiameter of 10 μm, pulse width in the range of 300 fs to 1.5 ps, a laserwavelength in the range of 1570 nm to 300 nm, the high fluence level wasdetermined to correspond to a pulse energy level of 1.5 μJ or more.

At operation 860, a beam from the laser operating at the first fluencelevel moves along a predetermined path to ablate trenches through themasking material, IC passivation, and thin film device layers to exposethe substrate. FIGS. 8B, 8C, and 8D illustrate cross-sectional views ofa substrate, such as that illustrated in FIG. 4A, as operations of thedicing method illustrated in FIG. 8A are performed, in accordance withan embodiment of the present invention.

FIG. 8B, the first pass of the laser operated at the first fluence levelat operation 860 ablates the trench 814A exposing the substrate 406along a first kerf width (KW₁). In the exemplary embodiment, the firstfluence is sufficient to ablate every layer of the thin film devicelayer stack 401 and therefore operation 103 leaves the substrate 406exposed at the bottom of the trench 414A. The kerf width KW₁ is afunction of a beam width possessing an intensity I₁ greater than athreshold associated for the particular materials in the thin filmdevice layer stack 401, particularly the dielectric layer threshold(T_(D)), as discussed above. For this reason, the mask 402, having alower threshold may have a kerf width (KW_(M)) which is wider than kerfwidth KW₁. As further shown in FIG. 8B, the operation 860 leaves splatsof residue 802 at the bottom of the trench 814A, which includesredeposited materials from the mask and IC passivation (e.g., organics).Metals and dielectrics from the thin film device layer stack 401 mayalso be incorporated with mask and passivation material in the residue802.

Returning to FIG. 8A, at operation 860 a second laser beam is generatedhaving a second irradiance that is lower than the first irradiance.Where the same pulse width is employed (e.g., femtosecond), thereduction in irradiance may be achieved with a reduction in fluence. Inparticular femtosecond embodiments, the fluence at operation 860 is nogreater than 1 μJ for a 10 μm diameter spot size, and preferably 0.75μJ, or less. This fluence level range is insufficient to ablatedielectric layers of the thin film IC stack (e.g., layers 504 and 507 inFIG. 5). In one particular embodiment with a focused spot diameter of 10μm, pulse width in the range of 300 fs to 1.5 ps, and laser wavelengthin the range of 1570 nm to 300 nm, a low fluence level was determined tobe 0.75 μJ, or less.

At operation 870, a beam from the laser operating at the second fluencelevel moves along the same predetermined path followed at operation 860to ablate trenches through the masking material, IC passivation, andthin film device layers to remove the spats of residue 802 left by theoperation 860. As further illustrated in FIG. 8C, the radiation 411 hasa second intensity I₂ less than that of I₁ (shown in dashed line asillustration of the difference between I₁ an I₂). As illustrated,because the second fluence level does not exceed the dielectric layerthreshold (TD), there is no additional direct ablation of the dielectriclayers and the kerf width KW₁ through thin film device stack 401 doesnot change significantly. However, because the thresholds associatedwith polymer materials typical for the mask and passivation are low, thesecond fluence level (irradiance) will remove residues over the entirefirst kerf width of the trench to provide a cleaner trench bottom 814B.

Returning to FIG. 8A, at operation 105, the plasma etch operation isperformed as described elsewhere herein. As further illustrated by FIG.8C, the plasma etch advances the cleaned trench bottom 814B through thesubstrate. With the splat residues 802 removed by the lower fluenceablation, the plasma etched trench has substantially the same kerf width(KW₁) as provided by the high fluence ablation. At operation 107 (FIG.8A) the mask may then be removed, as described elsewhere herein.

It should be noted that high-fluence-first embodiments exemplified bymethod 801 may be implemented with any of the techniques and hardwaredescribed elsewhere herein in terms of an exemplary low-fluence-firstprocess. For example, in one embodiment the iterative ablatingoperations 860 and 870 may be performed with multiple passes with a samelaser operating at different fluence levels or with multiple lasersperforming one or more pass. Similarly, beam shaping techniques may beperformed to vary the spatial profile of the beam. For example,direction of travel may be reversed from that shown in FIG. 3B to affecta high-fluence-first process rather than a low-fluence-first process.Similarly, all the hardware illustrated in FIGS. 6A, 6B and 7 describedin the context of a low-fluence-first embodiments (i.e. low-irradiancefirst process where pulse width is fixed) may be operated insubstantially the same manner to implement high-fluence-firstembodiments.

As an alternative to the multi-step method 801 which either involves apower re-adjustment or a second laser for the second pass (operations265 and 870), higher throughput may be achieve with the multi-stepmethod 901 illustrated in FIG. 9A which employs a beam splitter. Theexemplary embodiment illustrated in FIG. 9A begins with a receipt of amask substrate at operation 101 and generation of a beam at operation201, as described elsewhere herein. At operation 965, the beam is splitinto leading and trailing beams of the different irradiance (fluence)levels, I₁, I₂ with I₁ and I₂ having the relative levels of anyembodiment described elsewhere herein. At operation 970, the split beamsare displaced in unison relative to the substrate along a predeterminedpath in any of the manners described herein. Depending on the directionof relative displacement between the substrate in relation to relativepower of the split beam spots, a high-fluence-first or high-fluence-lastiterative scribing method may be implemented with a single pass. In theexemplary embodiment, the split beam method 901 implements ahigh-fluence-first scribing method. Method 901 completes die singulationwith the plasma etch and mask removal operations 105 and 107, aspreviously described.

Any commercially available variable beam splitter may be utilized foroperation 965. For example, in one embodiment a coated disk of glass inwhich the reflectivity of the coating varies angularly, so that onrotating the disk one can select the desired power ratio between twobeams produced by the device. In a further embodiment, a diffractiveoptical element (DOE) is employed where a phase grating concentratesmost of the laser energy on two diffraction orders. In an embodimentwhere a diffractive beam splitter is used to duplicate a master beaminto multiple replica beams having diameters equal to that of the inputbeam and positioned in a one- or two-dimensional array at well-specifiedangles, the phase profile of the beam generated at operation 201 ischosen so that the power ratio between the diffraction orders has aprescribed value. In further embodiments, different power ratios betweenproduced replicas may be chosen on adjacent diffracting elements of thegrating. Accordingly, a lateral shift in position of the DOE selects thedesired value of the power ratio between the multiple beam replicas usedto implement split beam method 901.

FIG. 9B illustrates a schematic diagram of a laser scribing module 900for split beam laser scribing, in accordance with an embodiment of thepresent invention. In FIG. 9B, the laser 902 provides the beam to a beamexpander and collimator 904. In one embodiment, the laser 902 isoperated at or close to the maximum pulse repetition rate which willdeliver a required pulse energy at each foci of a M×N dot matrix.Optionally, the beam may be passed through a Gaussian to top-hat beamshaping module 906, however such profile conversion will typically loseat least 30% of the incoming power, which may not be acceptable forfemtosecond embodiments in which power is already relatively lowcompared to picosecond sources, for example. The resulting beam, eitherfrom beam expander and collimator 904 or from the Gaussian to top-hatbeam shaping module 906, or both, is passed through variable beamsplitting module 908 with the split beams then passing through atelecentric lens 910 for transmission onto a substrate 912 so that thefocused spot-to-spot distance equals to the required die size forscribing in at least one dimension.

As illustrated by the B-B view of the beam spot pattern in FIG. 9B, thebeam is split into leading and trailing beams of the differentirradiance (fluence) levels, I₁, I₂ with I₁ and I₂ having the relativelevels of any embodiment described elsewhere herein. Depending on thedirection of relative displacement between the substrate 912 in relationto relative power of the split beam spots illustrated in the B-B view ofFIG. 9B, a high-fluence-first or high-fluence-last iterative scribingmethod may be implemented with a single pass. In the exemplaryembodiment shown in FIG. 9B, the illustrated scribing directionimplements the high-fluence-first scribing method. Although shown assquare patterns in FIG. 9B, it is to be understood that the A-A view andB-B view may also be rectangular in pattern, etc.

FIG. 10 further illustrates a diffractive beam splitting apparatus 1000,in accordance with an embodiment of the present invention. An incidentlaser 1002 passes through the diffractive optical element (DOE) 1004with a focusing lens 1006 having multiple foci provides multiple beams,points or spots to a working area 1008. In one embodiment, the focusinglens 1006 is telecentric to ensure the incident beam point is deliveredperpendicularly onto a work surface since there may exist a non-zerosplit angle subsequent to splitting the laser beam through, e.g., adiffractive beam splitter. In one such embodiment, a telecentric focallens of appropriate focal length is employed to provide N×N beams with apitch in one dimension equal to d, a pitch of streets between aplurality of ICs.

Thus, methods of dicing semiconductor substrates, each substrate havinga plurality of ICs, have been disclosed. The above description ofillustrative embodiments of the invention, including what is describedin the Abstract, is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. While specific implementationsof, and examples for, the invention are described herein forillustrative purposes, various equivalent modifications are possiblewithin the scope of the invention, as those skilled in the relevant artwill recognize. The scope of the invention is therefore to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

1. A method of dicing a substrate comprising a plurality of ICs, themethod comprising: receiving the substrate with an unpatterned maskcovering and protecting the ICs; ablating with a laser a predeterminedpattern of trenches into the mask and into a thin film IC stack disposedbelow the mask to expose a portion of a substrate, the ablating leadingwith electromagnetic radiation having a first irradiance and followingwith electromagnetic radiation having a second irradiance, lower thanthe first; and plasma etching the through substrate exposed by thepatterned mask trenches to singulate the ICs.
 2. The method of claim 1,wherein the electromagnetic radiation is from a single laser having apredetermined pulse width, the first irradiance associated with a firstpass of the laser operated at a first fluence that is higher than asecond fluence associated with the second irradiance.
 3. The method ofclaim 2, wherein the first fluence is sufficient to ablate a dielectriclayer of the thin film IC stack and wherein the second fluence isinsufficient to ablate the dielectric layer.
 4. The method of claim 2,wherein the first fluence is greater than 1.0 μJ for a 10 μm diameterspot size and wherein the second fluence is less than 1.0 μJ for a 10 μmdiameter spot size, with a pulse width between 300 fs and 1.5 ps.
 5. Themethod of claim 1, wherein the electromagnetic radiation with the firstirradiance forms a trench in the mask having a first kerf width andwherein the electromagnetic radiation with the second irradiance removesresidues within the first kerf width of the trench.
 6. The method ofclaim 1, wherein the ablating further comprises ablating the unpatternedmask, a polymeric passivation layer disposed below the unpatterned mask,and the thin film device stack with the radiation having the firstirradiance, and ablating redeposited polymeric mask or passivationmaterial with the radiation having the second irradiance.
 7. The methodof claim 2, wherein the ablating comprises a laser having a wavelengthless than or equal to 540 nanometers and a pulse width less than orequal to 400 femtoseconds.
 8. The method of claim 1, wherein theablating comprises splitting a beam from the laser into an array ofbeams, wherein a first beam of the array has the first irradiance and asecond beam of the array has the second irradiance.
 9. The method ofclaim 8, wherein the array of beams is two dimensional with pitch of thebeams in at least one dimension equal to a pitch of streets separatingadjacent ones of the plurality of ICs
 10. The method of claim 1, whereinthe substrate is silicon and the plasma etching comprises an anisotropicdeep silicon etch process employing a cyclic etch and polymer depositionprocess.
 11. A system for dicing a semiconductor substrate comprising aplurality of ICs, the system comprising: a laser scribe module topattern a mask and expose regions of a substrate between the ICs along apredetermined path, the laser scribe module to ablate a predeterminedpattern of trenches into the mask and into a thin film IC stack disposedbelow the mask by leading with a first irradiance and following withsecond irradiance, lower than the first; a plasma etch module physicallycoupled to the laser scribe module, the plasma etch module to singulatethe ICs by anisotropic plasma etching of the substrate; and a robotictransfer chamber to transfer a laser scribed substrate between the laserscribe module and the plasma etch module in vaccuo.
 12. The system ofclaim 11, wherein the laser scribe module comprises at least one laserhaving a wavelength less than or equal to 540 nanometers and a pulsewidth of less than or equal to 400 femtoseconds.
 13. The system of claim12, wherein the at least one femtosecond laser is to operate with thefirst fluence during a first pass along the predetermined pattern, thefirst fluence being greater than 1.0 μJ for a 10 μm diameter spot size.14. The system of claim 13, wherein the laser scribe module comprises asecond laser having a wavelength less than or equal to 540 nanometersand a pulse width of less than or equal to 400 femtoseconds, the secondlaser to operate with the second fluence during a second pass along thepredetermined pattern, the second fluence being less than 1.0 μJ for a10 μm diameter spot size.
 15. The system of claim 11, further comprisinga beam splitter configured for splitting a laser beam from the laserinto an M×N array of beams, where a first beam of the array has thefirst irradiance and a second beam of the array has the secondirradiance.
 16. The system of claim 15, wherein the beam splitterfurther comprises a diffractive optical element.
 17. A method of dicinga silicon substrate comprising a plurality of ICs, the methodcomprising: receiving a substrate with a mask covering and protectingthe ICs; ablating, with a first femtosecond laser pass having a firstirradiance, a predetermined pattern of trenches through the mask andthrough a thin film IC stack disposed below the mask to expose a portionof a substrate; ablating, with a second femtosecond laser pass having asecond irradiance, redeposited polymeric mask or passivation material inthe trenches left by the first femtosecond laser pass; and plasmaetching through the silicon substrate exposed by the patterned masktrenches to singulate the ICs.
 18. The method of claim 17, wherein thetrenches in the mask are ablated with a first kerf width and wherein theredeposited polymeric mask or passivation material is removed fromtrenches with substantially the same first kerf width.
 19. The method ofclaim 17, wherein the first femtosecond laser pass has a fluence greaterthan 1.0 μJ for a 10 μm and wherein the second femtosecond laser passhas a fluence less than 1.0 μJ for a 10 μm diameter spot size.
 20. Themethod of claim 17, wherein the first and second femtosecond laserpasses are both performed with a single laser.